The goal of this project is to contribute towards a comprehensive understanding of the biochemical and genetic parameters governing tRNA function and codon recognition in the genetic code. We will examine the following questions: 1) Codon recognition by E. coli tRNA-Ser and tRNA-Leu families of tRNAs under "normal" conditions; 2) the effects of ribosomal mutations on tRNA coding properties, including mutations in ribosomal flexibility and relaxed mutants; 3) the analysis of misreading phenomena under conditions when a specific aminoacylated tRNA is absent, either due to a tRNA-synthetase mutation or due to amino acid "starvation" in vitro; 4) codon recognition by mutant and undermodified tRNAs, obtained from cells with mutations in tRNA modification enzymes, or from relaxed auxotrophic cells subjected to nutritional manipulations; and 5) examination of effects of rate-limiting elongation upon protein synthesis, either by substrate limitation in tRNA-synthetase deficient extracts, or by tRNA mutations leading to partial growth defects of phage.